In UMTS, the allocation of the available transmission resources for HSDPA accesses, which in this case are codes, is typically operated to a plurality of terminals. These available resources are listed within a list consisting of 15 available codes. According to the UMTS specifications, it is required that each set of codes is in a single contiguous block, meaning that the code numbers for a single terminal are consecutive. Then, for signalling these sets of available resources, it is only required to have two parameters, namely, a starting point in the list, and a number of codes allocated to this terminal.
Currently, the UMTS specification for HSDPA in FDD mode describes signalling using 7 bits for the CCS (Channelization Code Set), as well as other parameters. For the case where the list of available resources comprises up to 15 codes, this allows all of the 120 possible configurations of starting code and number of codes to be indicated.
These 120 possibilities are illustrated in FIG. 1, where for each row representing an allocated number of codes, each darkened cell represents one possible value for the starting point.
Then, each mobile terminal using HSDPA is required to monitor up to four control channels (HS-SCCH) in case one of them carries control information intended for that terminal.
In practice, less than the maximum possible number of codes may have been allocated by the network for HSDPA data transmission. However, the current HS-SCCH signalling can address the whole code space.
However, the amount of signalling overhead for UMTS is potentially significant, and it is required to minimize the number of bits used for the signalling.